Radiation therapy aims at complete destruction of the proliferative capability of all clonogenic tumor cells, while not exceeding the tolerance for radiation damage to any of the tissues and organs. The biological effects depend on the amount and distribution of absorbed dose. Clinical dosimetry depends almost entirely on an underlying theoretical model. In chest irradiation; the field size, and shape dependent dose distribution is further determined by the size and shape of the patient, as well as density distribution, and inside the irradiated volume. The need for accurate accounting for the latter is still not unequivocally recognized. The present project is designed to shed new light on this problem. The dosimetry of a large number of patients is being investigated using computer generated dosimetry, as well as relevant measurements.